LDAP is really funky. Took me quite a while to get it all going stable with my company. You should first know your Base DN, include that in the search, then do a search on yourself.
No saying this will work for you, but here is what I did...
$ldapConnect = ldap_connect("active_directory_server");
$ldapBin = ldap_bind($ldapConnect, "username", "password");
$ldapSearch = ldap_search($ldapConnect,"baseDN","(searchFor=KownField)");
ldap_set_option($ldapConnect, LDAP_OPT_PROTOCOL_VERSION, 3);
ldap_set_option($ldapConnect, LDAP_OPT_REFERRALS, 0);
$ldapInfo = ldap_get_entries($ldapConnect, $ldapSearch);
// this will create an array for you
// to find out what you can access
print_r($ldapInfo[0]);
HTH